The present invention relates to a work pickup apparatus in, e.g., a robot and, more particularly, to a work pickup apparatus for picking up a work using a plurality of parallel pickup pawls.
As a conventional work pickup apparatus, an apparatus in which chuck teeth are meshed with a groove worked in a spiral shape like in a chuck device such as a lathe is known.
In Japanese Patent Publication No. 64-3610 or Japanese Utility Model Laid-Open No. 63-136846, radial guide grooves b are formed in a disk-like member a, and pickup pawls d are engaged with a cam plate c, as shown in FIG. 1 as a prior art.
However, since these prior art devices employ the spiral plate and the cam plate, respectively, they suffer from the following drawbacks. That is,
1. The spiral plate and the cam plate are difficult to design.
2. The spiral plate and the cam plate are difficult to manufacture and expensive.
3. The spiral plate and the cam plate have large weights.
4. When a stroke of each pickup pawl is increased, the sizes of the spiral plate and the cam plate are increased accordingly, resulting in an increase in weight.
More specifically, radial moving paths l.sub.1, l.sub.2, and l.sub.3 of three finger members d.sub.1, d.sub.2, and d.sub.3 are set to be separated from each other at a separation angle of 120 degrees with respect to the center of the disk-like member a. For this reason, for example, a work having a triangular shape or non-parallel surfaces contacting finger members cannot be reliably picked up. When a large number of works f stored in a pallet e are to be picked up, a gap g.sub.1 between a work f.sub.1 to be picked up and an obliquely right upward adjacent work f.sub.2 in FIG. 2 has a sufficient margin. However, gaps g.sub.2 and g.sub.3 between the work f.sub.1 and its left and downward adjacent works f.sub.3 and f.sub.4 are small.
As a result, since the separation angle of the moving paths l.sub.1, l.sub.2, and l.sub.3 of the three finger members d.sub.1, d.sub.2, and d.sub.3 is fixed to a constant angle of 120 degrees, one finger member d.sub.1 can be inserted in the relatively large gap g.sub.1, but the remaining two fingers d.sub.2 and d.sub.3 cannot be respectively inserted in the small gaps g.sub.2 and g.sub.3. In this manner, it is impossible for the three finger members d.sub.1, d.sub.2, and d.sub.3 to pick up the work f.sub.1, thus posing a problem.
In the conventional pickup apparatus shown in FIG. 1, the finger members d.sub.1, d.sub.2, and d.sub.3 have the same synchronous moving strokes. In the state of the work f.sub.1 shown in FIG. 2, even if the finger members d.sub.2 and d.sub.3 can be inserted in the small gaps g.sub.2 and g.sub.3, since the finger members d.sub.1, d.sub.2, and d.sub.3 have the same long moving strokes, the work f.sub.1 to be picked up is pushed in an obliquely right upward direction in FIG. 2, and pushes out right and upward adjacent works f.sub.5 and f.sub.6 (FIG. 3A) from their positions. In this manner, the placing positions of the works f.sub.5 and f.sub.6 in the pallet e are shifted, and the pickup operations of these works f.sub.5 and f.sub.6 are disabled.
When the works f.sub.5 and f.sub.6 are placed to be inserted on the bottom surface of the pallet e, a movement of these works along a horizontal surface is inhibited. For this reason, when the work f.sub.1 is pushed in an obliquely right upward direction upon its pickup operation in such a placing state, its movement is blocked by the works f.sub.5 and f.sub.6, as shown in FIG. 3B. As a result, the work f.sub.1 cannot be picked up.